Variable resistor



2 sheets-sheet 1 K. W. JARVIS VARIABLE REsIsToR nnlnnAAn/lnlullllnnnnnnlNov. 18, 1958 Filed Aug. 27, 1956 nllnllhhlnnnl M TIE. El f Nov. 18,1958 K. w. JARvls 2,851,158

VARIABLE RESISTOR Filed Aug. 27, 1956 4 2 Sheets-Sheet 2 FII- i5 UnitedStates Patent 'C VARIABLE RESISTOR Kenneth W. Jarvis, Winnetka, Ill.

Application August 27, 1956, Serial No. 606,407

15 Claims. (Cl. 201-48) The present invention relates to variableresistors, particularly variable resistors for use in devices requiringrelatively small currents, such as electronic equipment.

Most variable resistors of this type are constructed with cards whichinclude a plurality of turns of resistance wire wound transverselyaround a strip of electrical insulating material. The card is usuallyprovided with an insulating coating except for anarrow strip whichextends along the card generally normal to the turns.v An electricalcontact is then mechanically mounted in slidable contact with the narrowstrip of exposed turns of resistance wire on the card.

There is an ever increasing demand for smaller electronic components.Unfortunately, resistance wire smaller than about size A. W. G. No. 45does not have sufficient mechanical strength to withstand the wear ofthe slidable contact nor sufcient current carrying capacity for manyapplications. It has thus been necessary to reduce the total resistanceof variable resistors in order to reduce their physical size. It is oneof the objects of the present invention to provide a smaller variableresistor than has presently been available in the art without reducingthe total resistance of the unit.

In the conventional annular construction of variable resistors, theresistance card is placed within a hollow cylindrical container andpositioned adjacent to the periphery of the container. disposed on theaxis of the cylindrical container and an arm is secured to the shaft andmounts the slidable contact abutting the exposed portion of the card.There is generally a volume of unused space between the shaft andtheresistance card. The inventor has found that this space can beutilized in order to increase the rey sistance of the variable resistor,or conversely, to reduce the length of the resistance card, and thus thesize of the unit. l

Further, it is an object of the present invention to provide a method ofproducing variable resistors which utilize the space between the shaftand the resistance card. The present invention will `be more fullyunderstood, together with further advantages and uses for the invention,from a further reading of this disclosure, particularly when viewed inthe light of the drawings, in whichz?H "Figurel `is a sectional view ofa variable resistor constructed according to the teachings of thepresent invention, the section being taken along the line 1-1 of Figure2;

Figure 2 is a sectional View ot' the variable resistor taken along theline 2--2 of Figure l;

Figure 3 is a transverse sectional view of the resistance card shown inFigures l and 2 before being assembled into the variable resistor;

Figure 4 is a sectional view taken along the line 4-4 of Figure 3;

Figure 5 is a sectional view taken along the line S--S of Figure 2showing the contact disc;

A rotatable shaft is then Figure 6 is a sectional view taken along theline 6 6 of Figure 2;

Figure 7 is an elevational view of a portion of a coil winding machinewith the resistance card of the variable resistor illustrated during theprocess of manufacture;

Figure 8 is an isometric view illustrating another step in themanufacturing process of the resistance card; and

Figure 9 is an alternative embodiment of a resistance card of the typehaving a step resistance to contact displacement characteristic.

The variable resistor illustrated in the figures has a hollowcylindrical casing 10 with a closed end 12 and an open end 14. A cover16 is secured to the open end 14 of the casing 10 by pressed titting thecover 16 within an indentation 18 in the open end 14 of the casingf10.The closed end 12 of the casing 10 is provided with a central apertureZtl, and has a sleeve 21 which extends toward the open end 14 of thecasing 10. A bushing 22 is secured to the casing 10 and disposed withinthe aperture 20 and sleeve 21. The bushing 22 has a hollow cylinder 24which extends into the sleeve 21 of the casing 10 coaxially therewith. Ashaft 26 is journaled within the cylinder 24 of the `bushing 22 andextends through an aperture 27 in the cover 16. The shaft 26 is providedwith a C-washer 28 secured within a groove 29 and abutting the bushing22, and a second C-Washer 30 disposed within a groove 31 and abuttingthe cover 16, thereby preventing translation of the shaft 26 within thebushing and limiting its motion to rotation.

The interior of the casing 10 is lined with an annular strip 32 ofelectrical insulating material which is secured to the interior surfaceof the casing 10; for example by a layer of cement 34. A resistance card36, which will be described in detail, is annular in form and disposedin Contact with the strip 32 of electrical insulating material.-

The resistance card 36 extends about the periphery of the interior ofthe casing 10 and is secured to the strip 32 by a layer of cement 37.

The resistance card 36 is provided with a strip 38 of electricalinsulating material which is disposed in an annular form Within thecasing 10. The strip 38 supports a plurality of turns 40 of resistancewire 42. The resistance Wire 42 is provided with a core 43 ofelectrically conducting wire of uniform resistivity and a coating 44 ofelectrically insulating material, such as enamel for example. A layer 46of electrically insulating adhesive material is also disposed about thestrip 38 and turns 40 except for the edge 48 of the resistance card 36which confronts the open end 14 of the container. This edge 48 is freeof insulating coating 46, and the turns 40 of resistance wire 42 arealso free of the electrical insulating coating 44.

In the embodiment of Figures l through 9, each of the turns 40 about thestrip 38 is longer than the distance about the periphery of the strip,and the excess portion of the turns, designated 47, extends outwardlyfrom the edge 50 of the resistance card 36 opposite to the edge 48. Thisoutwardly extending portion 47 is also covered by the adhesive layer 46,and is wound into coils 54 which are disposed between the resistancecard 36 and the sleeve 21 of the casing 1G. The interior of the casing1t) contains a layer 56 of potting compound from the closed end 12 ofthe casing 10 to a level adjacent to adjacent toits periphery. Eachcontact member 60 has a wire shaped contact 62 which is disposedabutting the exposed portion of the turns 40 on the edge 48 of theresistance card 36.

Each contact member 60 has a support bar 64 constructed of electricallyconducting material which is secured to the electrical insulating disc58 in a peripheral indentation 65 and is disposed generally parallel tothe periphery of the disc S, for example, by a pair of screws 66disposed at the ends of the support bar 64. The support bars 64 are eachprovided with an indentation 68 on the side confronting the resistancecard 36, and a pair of aligned screws 70 and 72 parallel to the axis ofthe support bar 64 are threadedly engaged within apertures 74 and 76extending through the support bars 64 into the indentation 68. A pin 32is pivotally disposed between screws '70 and 72.

The illustrative embodiment of contact 62 shown in the drawing is in theform of a ridged electrically conducting wire which is secured to theends of the pin 82 and makes electrical contact with the pin 82, forexbar 64 to place a spring bias upon the contact 62 in the In thismanner, the

direction of the resistance card 36. central portion 86 of each contactmember 62 is maintained in abutment with the exposed turns 4t) on theedge 4S of the resistance card 36. The above-described construction ofcontact member 60 and contact 62 is intended to be merely illustrativeand it is contemplated that various other equally advantageousconstructions may be devised by those skilled in the art.

The electrical insulating disc 58 also supports a pair of concentricelectrically conducting rings 94 and 95 which are coaxially disposedabout the shaft 26 on the side of the disc 58 confronting the closed end12 of the casing 10. The ring 94 is electrically connected to one of thecontact members 60 and the ring 95 is connected to the other contactmember 60 by wires 96.

The conducting rings 94 and 95 are each in slidable contact with a pairof contact asemblies 97 and 99 which have a pair of electricallyconducting contacts 98 and 100 of a take-off assembly 102. The take-oftrassembly 102 has an electrically insulating block 104 which is mountedto the end 12 of the casing 10 confronting the conducting rings 94 and95, as illustrated in Figure 2. A pair of parallel slots 106 and 107generally parallel to the confronting of the conducting rings 94 and 95are disposed in the surface of the block 104 confronting the conductingrings 94 and 95. Each of the contacts 98 and 100 are mounted at the endsof arms 108 and 110, respectively, which are constructed of electricallyconducting material. Each pair of arms 108 and 110V is pivoted at apoint between their ends on a pin 112 which extends into the block 104of insulating material normal to the arms 108 and 110 and through one ofthe slots 106 in the block 104. A helical spring 114 is disposed aboutthe pin 112 between each pair of arms 10S and 110. One end of eachspring 114 is attached to the end of arm 108 opposite to the contact 98,and the other end of each spring 114 is attached to the adjacent arm 11?opposite the contact 100, thereby spring-biasing these ends of the arms103 and 110 toward the slot 106, or in other words, spring biasing thecontacts 98 and 100 outwardly from the slot 106.

The arms S and 110 of each contact assembly 97 and 99 are electricallyinterconnected by the pins 112. Also, one of the arms 108 of contactassembly 97 is connected to a terminal 116, and the arm110 of contactassembly 99 is connected to a terminal 118. Electrical contact to theother arm of each pair of arms 1s made through the pins 114. Electricalconnections may be made to these terminals 116 and 113 and to one ormore points on the resistance card, in the conventional manner.

It is to be understood that the invention can be practiced with any typeof contact to the resistance card 36, but that the contacts 60 heredisclosed are particularly satisfactory. Also, the invention may bepracticed with other means to make electrical contact with the slidablecontact in place of the take-off assembly 102, even though the take-offassembly 102 is of particular advantage.

The inventor has found that a preferred method of manufacturing thevariable resistor described in Figures l through 6 is to mount theelectrically insulating strip 3S which is to become a part of theresistance card 36 between the chucks 126 and 123 of a coil windingmachine, and mount a second strip 130 in the same plane with the strip33 adjacent thereto, as illustrated in Figure 7. Operation of the coilwinding machine will then place the turns 40 of resistance wire aroundthe combined strips 38 and 130, the portions of each of the turns 40which are disposed adjacent to the strip 130 becoming the outwardlyextending portions 47, illustrated in Figure 3. After the turns 40 ofresistance wire are placed upon the strips 3B and 130, the wire 42 beingcoated with the electrically insulating coating 44 before winding, theturns 40 are coated with the layer 46 and cemented to the strip 38.

The portion of the turns 40 which are adjacent to the strip 130 arecoated with the layer 40 to bind them together, ybut this portion ofthese turns 40 are not cemented to the Strip 130. The strips 33 and 130are then removed from the chucks 126 and 128 of the winding machine, andthe strip 130 is withdrawn from the turns 40. The strip 130 hascompleted its purpose and forms no further portion of the manufacturingprocedure, or the finished product. The strip 38 is then taken and theoutwardly extending portion 47 of the turns are separated into smallgroups, designated 132 in Figure 8, and wound up on dowels 134. Thedowels 134 are then removed, leaving a plurality of small windings ofturns which are kept together by the adhesive layer 46 thereon. The edge48 of the strip 36 is then cleaned, the electrically insulating layer46, and the coating 44 of varnish or other electrically insulatingmaterial being removed so that the contact 62 will be able to make goodelectrical contact with each of the turns 40 when it is disposed incontact therewith. All of the small coils 54 are then positioned on thesame side of the strip 36, and the strip is placed within the container10 and bent into the annular form it must assume to t against theelectrically insulating strip 32.

After the resistance card 36 is cemented into the casing 10, thetake-off assembly 102 is mounted to the closed end 12 of the casing llt.This can be most readily accomplished by inserting a pin or screw 140,shown in Figure 6, through an aperture 142 in the closed end of thecasing 10`and a bore 144 in the block 104 provided for the lpurpose ofaligning the take-off assembly with the contact rings 94 and 95. Thepotting compound 56 is then poured into the closed end 12 of the casing10 until the level of the compound 56 approaches the end of the casingsleeve 21 confronting the open end 14 of the casing 10, thus coveringand anchoring the coils 54. After the potting compound 56 hardens, thepin or screw may be removed, the potting compound holding the take-olfassembly 102 in place.

The disc 58 and shaft 26 are assembled, the hub 59 being rstconveniently secured to the disc 58 by screws 146 extending through thedisc 58 and threaded intoA the hub 59. The contact members 60 are alsofastened to the disc 58 by theV screws 66. The assembled shaft26 anddisc 58 are then inserted into the casing 10, and the C-washer 28 put inplace. Next the cover 16 is pressed into the groove 18, and the C-washer30 inserted into the groove 31 in the shaft 26.

If a stop on rotation of the shaft is desired, an angle bracket 148 issecured to the disc 58 confronting `the closed end 12 of the casing 10,and the bracket is provided with an outwardly extending portion 150which is generally normal to the disc 58. A post 152 is secured to theclosed end 12 of the casing 10 and projects above the level of thepotting compound 56 to abut the portion 150 of the bracket 148, thusproviding the desired stop.

The variable resistor described above has a lineal' resistance tocontact displacement characteristic. A variable resistor may be providedwith other characteristics by shaping the strip 130 to provide coils ofdifferent length. The dotted line in Figure 7 indicates a strip 130Awhich has one straight edge abutting strip 38, and one edge graduated insteps, thereby providing a step resistance to contact displacementcharacteristic. The manner in which strip 130A cooperates with strip 38is better seen in Figure 9. It is also to be noted that a portion of theturns 40 do not extend around the strip 130A, but merely extend aboutthe strip 38.

From the foregoing disclosure, the man skilled in the art will readilydevise many modifications and additional applications for the presentinvention beyond those disclosed herein. For example, the presentinvention may be practiced with the particular contact mechanism formaking contact with the resistance card disclosed herein, or practicedwith more conventional contact mechanisms. Further, the invention may bepracticed either with or without the particular contact ring take-olfassembly here described. For these reasons, it is intended that thescope of the present invention be not limited by the foregoingdisclosure, but rather only by the appended claims.

AI claim as my invention:

l. A variable resistor comprising an elongated strip of electricallyinsulating material, a coil of resistance wire wound about the strip andsecured to the strip, said coil having a plurality of turns withadjacent portions of each turn electrically insulated from each otherand each turn substantially longer than the distance around theperimeter of the strip, and means to make electrical contact with theresistance wire including a slidable contact confronting the strip andabutting the turns of said coil.

2. A resistor comprising a hollow cylindrical casing, an elongated stripof electrically insulating material disposed concentrically within thecasing, a coil of resistance wire wound about the strip and secured tothe strip, said coil having a plurality of turns with adjacent portionsof each turn electrically insulated fro each other and each turnsubstantially longer than the distance around the confronting perimeterof the strip, whereby each turn has an outwardly extending portion, saidoutwardly extending portions being electrically insulated from eachother and from the other elements of the resistor and being disposedbetween the strip and the axis of the casing.

3. A variable resistor comprising the elements of claim 2 in combinationwith a shaft rotatably mounted on the axis of the casing, and anelectrical contact mounted to the shaft and slidably disposed abuttingthe portion of the coil adjacent to the strip.

4. Available resistor comprising a hollow cylindrical casing closed atone end, a shaft rotatably mounted to the casing and disposed on theaxis thereof, an elongated strip of electrically insulating materialdisposed concentrically about the shaft, a coil of resistance wire woundabout the strip and secured thereto, said coil having a plurality ofturns with adjacent portions of the turns electrically insulated fromeach other, each of said turns being substantially longer than theconfronting perimeter around the strip and having an outwardly extendingpor-f tion disposed between the shaft and the strip, a mass of pottingcompound disposed over the outwardly extending portion of the coil ofresistance wire in the closed end of the casing, an electrical contactmounted to the shaft and slidably disposed in abutment with the coil ofresistance wire along a path confronting the strip,- a terminal mountedto the casing, and electrically conducting means to connect the slidablecontact with the terminal.

5. A variable resistor comprising a cylindrical hollow container havingone end provided with a central aperture, a shaft disposed on the axisof the container and rotatably journaled in the aperture in the endthereof, a strip having parallel faces and parallel edges annularlydisposed within and adjacent to the periphery of the container, aplurality of turns of resistance wire disposed about the strip andsecured to the faces and one edge thereof, said turns being secured tothe strip in parallel spaced apart insulated relationship and extendingoutwardly from the other edge of the strip, a `coating of electricallyinsulating material covering the strip and windings except for a bandgenerally normal to the turns and spaced from the apertured end of thecontainer, and an electrical contact mounted to the shaft and slidablyabutting the uncoated band of windings.

6. A variable resistor comprising a cylindrical hollow containerconstructed of electrically conducting material having one end providedwith a central aperture, a shaft disposed on the axisof the containerand rotatably journaled in the aperture in the end thereof, a strip ofelectrical insulating material having parallel faces and generallyparallel edges, said strip being annularly disposed within and adjacentto the periphery of the container, an electrically insulating memberdisposed between the strip and the container, a plurality of turns orresistance wire disposed about the strip and secured to the faces andone edge thereof, said turns extending outwardly from the other edge ofthe strip in the region between the strip and shaft and being secured tothe strip in parallel spaced apart insulated relationship, a coating ofelectrical insulating material covering the strip and windings exceptfor a band generally normal to the turns and spaced from the aperturedend of the container, a mass of electrical insulating material disposedin the container covering the outwardly extending portions of thewindings, and an electrical contact mounted to the shaft slidablyabutting the uncoated band of windings.

7. Arvariable resistor comprising a cylindrical hollow container havingone end provided with a central aperture, a shaft disposed on the axisof the container and rotatably journaled in the aperture in the lendthereof, a strip having parallel faces and generally parallel edgesannularly disposed within and adjacent to the periphery of thecontainer, a plurality of turns of resistance wire disposed about thestrip and secured to the faces and one edge thereof, said turnsextending outwardly from the other edge of the strip and being securedto the strip in parallel spaced apart insulated relationship, theoutwardly extending portions being wound into a plurality of coils anddisposed in the region between the strip and shaft, a coating ofelectrical insulating material covering the strip and windings securedthereto except for a band generally normal to the turns and spaced fromthe apertured end of the container, and an electrical contact mounted tothe shaft slidably abutting the uncoated band of windings.

8. The method of manufacture comprising the steps of securing the endsof a rst and second at elongated strip adjacent to each other in acommon plane, placing the ends of said strip in a winding machine andwinding a plurality of turns of resistance wire tightly about both ofsaid strips generally normal to the axis of elongation thereof, removingthe strips from the winding machine, securing the turns abutting onestrip thereto, and

7 removing the second strip from the first strip and turns, whereby theturns have -portions secured to the strip and portions extendingoutwardly therefrom.

9. The method of manufacture comprising the steps of securing a firstand a second at elongated strip adjacent to each other in -acommonplane, winding a plurality of turns of resistance wire tightly aboutvboth of said strips generally normal to the axis of elongation thereof,securing the `turns abutting vthe first strip thereto, and removing thesecond strip from the turns and iirst strip, whereby the turns haveVportions secured to the first strip and portions extending outwardlytherefrom.

1'0. A variable resistor comprising a cylindrical hollow containerhaving one end provided -with Aa central aperture, a shaft disposed Ionthe axis -of the conta-incr and rotatably journaled in the aperture inthe end thereof, a strip having parallel faces and generally paralleledges disposed within and adjacent to the periphery of the container, aplurality of turns -of Vresistance wire disposed about .the strip andsecured to the faces and one edge thereof, said turns extendingoutwardly from the other edge of the strip and being secured to thestrip in parallel spaced apart insulated relationship, the outwardlyextending portions being wound into a plurality of coils and disposed inthe region between the strip and shaft, a layer of electrical insulatingmaterial covering the strip and windings secured thereto except for aband generally normal to the turns and spaced from the apertured end ofthe container, a mass of electrical insulating potting compound disposedin the container covering the outwardly extending portions of thewindings, and an electrical contact mounted to the Vshaft slidablyabutting the uncoated band of the windings.

ll. The method of manufacture compiising the steps of securing a firstand second flat elongated strip adjacent to each other in a commonplane, winding a plurality of turns -of resistance wire tightly aboutboth of said strips generally normal to the axis of elongation thereof,securing the turns abutting the first strip thereto, removing the secondstrip from the turns and first strip, whereby the turns have portionssecured to the first strip and portions extending outwardly therefrom,winding the outwardly extending portions of the turns into coils toreduce the space required therefor, bending the strip and turns into acylindrical shape, and inserting the strip and turns into a cylindricalcontainer.

l2. The method of manufacture comprising the steps of securing a firstand second dat velongated strip adjacent to each other in a lcommonplane, winding aplurality of turns of resistance wire tightly about bothof said strips generally normal to the axis of elongation thereof,scouring the turns abutting the rst strip thereto, removing the` secondstrip from the turns and Vfirst strip, whereby the turns have portionssecured to the first strip and portionsextending outwardly therefrom,winding the outwardly extending portions of the turns into coils toreduce the space required therefor, bending' the strip and turns into acylindrical shape, inserting the strip and turns into a cylindricalcontainer, and filling the container with .a potting compound to a levelabove lthe outwardly extending portion of the turns and below the top ofthe strip.

13. The method of manufacture comprising the steps of securing a firstand second fiat elongated strip adjacent to each other in a commonplane, winding a plurality of turns of resistance wire having anelectrically insulating covering tightly about both of said stripsgenerally normal to the axis of elongation thereof, securing the turnsabutting the lirst strip thereto, coating the 'turns with anelectrically insulating adhesive material, coating the portion of theturns secured to the first strip with an electrically insulatingmaterial, removing the second strip from the turns and first strip,whereby the turns have portions secured to the first strip and portionsextending outwardly therefrom, removing the electrically insulatingcoating from the turns in a band generally parallel to the edges of thestrip, winding up the outwardly assembled portions to reduce the spacerequired therefor, bending the strip and turns into a cylindrical shape,inserting the strip and vturns into a cylindrical container, and fillingthe container with a potting compound to a level above the outwardlyextending portion of the windings and below the top of the strip.

14. A variable resistor comprising an elongated strip of .electricallyinsulating material, a coil of resistance wire wound about the strip andsecured to kthe strip, said coil having a plurality of turns withadjacent portions of each turn electrically insulated from each otherand at least a portion of the turns being substantially longer than thedistance around the perimeter of the strip, and means to make electricalcontact with the resistance wire including a slidable contactconfronting the strip and abutting the turns of said coil.

l5. A variable resistor comprising an elongated strip of electricallyinsulating material, a coil of resistance wire wound about the strip andsecured to the strip, said' coil having a plurality of turns withadjacent portions of each turn electrically insulated from each other,at least a portion of said turns being substantially longer than thedistance around the perimeter of the strip, and said longer portionhaving a plurality of different length turns, and means to makeelectrical contact with the resistance wire including a slidable contactconfronting the strip and abutting the turns ofthe coil.

References Cited in the `lile of this patent UNITED STATES PATENTS1,171,059 Longuin Feb. 8, 1916

